Method of producing crystalline semiconductor material and method of fabricating semiconductor device

ABSTRACT

Disclosed are a method of producing a crystalline semiconductor material capable of improving the crystallinity and a method of fabricating a semiconductor device using the crystalline semiconductor material. An amorphous film is uniformly irradiated with a pulse laser beam (energy beam) emitted from an XeCl excimer laser by 150 times so as to heat the amorphous film at such a temperature as to partially melt crystal grains having the {100} orientations with respect to the vertical direction of a substrate and melt amorphous film or crystal grains having face orientations other than the {100} orientations. Silicon crystals having the {100} orientations newly occur between a silicon oxide film and liquid-phase silicon and are bonded to each other at random, to newly form crystal grains having the {100} orientations. Such a crystal grain creation step is repeated, to form a crystalline film which has crystal grains preferentially grown in the {100} orientations with respect to the vertical direction of the substrate and thereby has sharp square-shaped crystal grain boundaries.

RELATED APPLICATION DATA

The present application claims priority to Japanese Application(s)No(s). P2002-242614 filed Aug. 22, 2002, which application(s) is/areincorporated herein by reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

The present invention relates to a method of producing a crystallinesemiconductor material by heating an amorphous semiconductor material ora polycrystalline semiconductor material so as to crystallize thematerial, and a method of fabricating a semiconductor device using sucha crystalline semiconductor material.

In recent years, semiconductor devices used, for example, for a solarcell including such semiconductor devices formed on a substrate in anarray pattern and for a liquid crystal display unit including suchsemiconductor devices as pixel drive transistors have been activelystudied and developed. Further, in recent years, to realize a highdegree of integration and multi-function of semiconductor devices, athree-dimensional integrated circuit including the semiconductor devicesstacked on a substrate has been actively studied and developed.

A glass material such as artificial quartz or a plastic material hasdrawn attention as a substrate material used for these semiconductordevices because the glass material or plastic material is inexpensiveand is easily formable into a large-size substrate. In general, when asemiconductor thin film is deposited on a substrate made from such anamorphous insulating material, since the amorphous insulating materialhas no long-range order, the deposited semiconductor thin film has anamorphous or polycrystalline structure.

For example, with respect to a thin film transistor (TFT) used as apixel drive transistor in a liquid crystal display unit, an operationalregion (channel region) is formed by a polycrystalline silicon (Si) filmformed on the above-described substrate. The use of the polycrystallinesilicon film for forming the operational region, however, has adisadvantage that the crystallinity of the polycrystalline silicon filmis poor because crystal grains boundaries are present at random in thefine structure of the film and crystal grains have different faceorientations. Another disadvantage is that as the grain sizes of crystalgrains in the polycrystalline silicon film become as large as beingclose to the channel length of the TFT, the characteristics of the TFTmay become uneven. In this way, a semiconductor device such as a TFTusing a polycrystalline silicon film is very inferior in characteristicsto a semiconductor device using a single crystal silicon film.

From this viewpoint, a single crystallization technique of a siliconfilm formed on a substrate made from a glass material has bee proposed.For example, an attempt has been made to form a single crystal siliconfilm on a substrate made from silicon oxide by using a ZMR (Zone MeltingRe-crystallization) technique (see H. A. Atwater et al.: Appl. Phys.Lett. 41 (1982) 747, or K. Egami et al.: Appl. Phys. Lett. 44 (1984)962). Another attempt has been made to form a silicon film having a verylarge area on a substrate made from quartz or glass (see A. Hara et al.:AMLCD Technical Digest p. 227, Tokyo 2002).

The ZMR technique allows formation of a silicon film having a largearea, but has a difficulty in control of orientation of crystal grainsand crystal grain boundaries. Accordingly, a silicon film formed by theZMR technique contains crystal grain boundaries that are present atrandom, and is therefore difficult to be applied to three-dimensionalintegration of semiconductor devices, which integration requires ahigh-level equalization of the semiconductor devices. Another problem ofthe ZMR technique is that since the ZMR technique is a high temperatureprocess requiring a large thermal load such as about 1450° C., such aZMR technique cannot be applied to a plastic material expected as asubstrate material. Taking into account the heat resistance of a plasticmaterial, a low temperature process performed at about 200° C. or lessis desirable.

In recent year, a method of producing a silicon film having crystalgrains grown in the {111} orientations on a buffer layer made fromsilicon nitride by laser irradiation using a second harmonic neodymiumlaser (Nd:YVO₄ laser) having a wavelength of 532 nm has been disposed(see M. Nerding et al.: Thin Solid Films 383 (2001) 110). This method,however, has an inconvenience that since a silicon film having crystalgrains grown in the {100} orientations has been used for a semiconductordevice in an advanced MOS transistor, the silicon film having thecrystal grains grown in the {111} orientations cannot be applied to aprocess of fabricating the above-described MOS transistor. In addition,the reason why the silicon film having crystal grains grown in the {100}orientations is used for the above-described semiconductor device isthat the silicon crystal grains having the {100} orientations are lowerin interface level density than silicon crystal grains having faceorientation other than the {100} orientations, and therefore, suitablefor forming a transistor sensitive to interface characteristics.

As described above, according to the related art techniques, it has beendifficult to control crystal grain boundaries of a crystalline filmformed on a substrate made from a glass material or plastic material, tocontrol the face orientations of crystal grains to specific faceorientations (for example, {100} orientations for a silicon film) withrespect to the vertical direction of the substrate, and to control faceorientations of the crystal grains in the in-plane direction of thesubstrate, thereby failing to equalize the quality of a semiconductordevice and sufficiently enhance the performance thereof.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of producing acrystalline semiconductor material, which is capable of forming asemiconductor material having good crystallinity at a low temperature ona substrate made from a glass material or plastic material, and toprovide a method of fabricating a semiconductor device using such acrystalline semiconductor material.

To achieve the above object, according to a first aspect of the presentinvention, there is provided a method of producing a crystallinesemiconductor material composed of a plurality of single-crystal grainsof a semiconductor, including a first step of forming an amorphousmaterial of the semiconductor or a polycrystalline material of thesemiconductor on a substrate, and a second step of forming a crystallinematerial by uniformly heat-treating the amorphous material or thepolycrystalline material by a plurality of times at such a temperatureas to partially melt crystal grains having a specific face orientationwith respect to the vertical direction of the surface of the substrateand melt the amorphous material or crystal grains having a faceorientation other than the specific face orientation.

According to a second aspect of the present invention, there is provideda method of producing a crystalline semiconductor material composed of aplurality of single-crystal grains of a semiconductor, including a firststep of forming an amorphous material of the semiconductor or apolycrystalline material of the semiconductor on a substrate, a secondstep of forming a first crystalline material by uniformly heat-treatingthe amorphous material or the polycrystalline material by a plurality oftimes at such a temperature as to partially melt crystal grains having aspecific face orientation with respect to the vertical direction of thesurface of the substrate and to melt the amorphous material or crystalgrains having a face orientation other than the specific faceorientation, and a third step of forming a second crystalline materialby heat-treating the first crystalline material by a plurality of timesso as to selectively form, on the first crystalline material, atemperature distribution having a high temperature region and a lowtemperature region whose temperature is lower than that of the hightemperature region, wherein the temperature of the low temperatureregion is set to partially melt the crystal grains having the specificface orientation.

According to a third aspect of the present invention, there is provideda method of fabricating a semiconductor device using a crystallinesemiconductor material composed of a plurality of single-crystal grainsof a semiconductor, including a first step of forming an amorphousmaterial of the semiconductor or a polycrystalline material of thesemiconductor on a substrate, and a second step of forming a crystallinematerial by uniformly heat-treating the amorphous material or thepolycrystalline material by a plurality of times at such a temperatureas to partially melt crystal grains having a specific face orientationwith respect to the vertical direction of the surface of the substrateand melt the amorphous material or crystal grains having a faceorientation other than the specific face orientation.

According to a fourth aspect of the present invention, there is provideda method of fabricating semiconductor device using a crystallinesemiconductor material composed of a plurality of single-crystal grainsof a semiconductor, including a first step of forming an amorphousmaterial of the semiconductor or a polycrystalline material of thesemiconductor on a substrate, a second step of forming a firstcrystalline material by uniformly heat-treating the amorphous materialor the polycrystalline material by a plurality of times at such atemperature as to partially melt crystal grains having a specific faceorientation with respect to the vertical direction of the surface of thesubstrate and to melt the amorphous material or crystal grains having aface orientation other than the specific face orientation, and a thirdstep of forming a second crystalline material by heat-treating the firstcrystalline material by a plurality of times so as to selectively form,on the first crystalline material, a temperature distribution having ahigh temperature region and a low temperature region whose temperatureis lower than that of the high temperature region, wherein thetemperature of the low temperature region is set to partially melt thecrystal grains having the specific face orientation.

In accordance with the method of producing a crystalline semiconductormaterial according to the first aspect and the method of fabricating asemiconductor device according to the third aspect, since the amorphousmaterial or the polycrystalline material are uniformly heat-treated by aplurality of times at such a temperature as to partially melt crystalgrains having a specific face orientation with respect to the verticaldirection of the surface of the substrate and melt the amorphousmaterial or crystal grains having a face orientation other than thespecific face orientation, it is possible to form a crystalline materialwhich has crystal grains preferentially grown in the specific faceorientation with respect to the vertical direction of the substrate andthereby has sharp crystal grain boundaries, and hence to improve thecrystallinity of the crystalline material.

In accordance with the method of producing a crystalline semiconductormaterial according to the second aspect and the method of fabricating asemiconductor device according to the fourth aspect, in the second step,a first crystalline material is formed by uniformly heat-treating theamorphous material or the polycrystalline material by a plurality oftimes at such a temperature as to partially melt crystal grains having aspecific face orientation with respect to the vertical direction of thesurface of the substrate and to melt the amorphous material or crystalgrains having a face orientation other than the specific faceorientation; and in the third step, a second crystalline material isformed by heat-treating the first crystalline material by a plurality oftimes so as to selectively form, on the first crystalline material, atemperature distribution having a high temperature region and a lowtemperature region whose temperature is lower than that of the hightemperature region, wherein the temperature of the low temperatureregion is set to partially melt the crystal grains having the specificface orientation. As a result, it is possible to form the secondcrystalline material having crystal grains preferentially grown in thespecific face orientation with respect to the vertical direction of thesubstrate and preferentially grown in a controlled face orientation inthe in-plane direction of the substrate, and hence to control thecrystal grain boundaries in the second crystalline material and improvethe crystallinity of the second crystalline material.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription in conjunction with the accompanying drawings, wherein:

FIG. 1 is a typical block diagram showing the structure of a liquidcrystal display unit fabricated by a method according to one embodimentof the present invention;

FIG. 2 is a view showing the structure of a sample used in theembodiment of the present invention;

FIGS. 3A to 3C are sectional views illustrating a first heat-treatment;

FIG. 4 is a diagram showing a schematic shape of one pulse of a pulselaser beam shown in FIG. 2;

FIG. 5A is a plan view illustrating the heating step shown in FIGS. 3Ato 3C, and FIG. 5B is a diagram showing a schematic shape of the pulselaser beam used for the heating step shown in FIGS. 3A to 3C;

FIG. 6A is a plan view illustrating the heating step shown in FIGS. 3Ato 3C, and FIG. 6B is a diagram showing a schematic shape of the pulselaser beam used for the heating step shown in FIGS. 3A to 3C;

FIG. 7A is a plan view illustrating the heating step shown in FIGS. 3Ato 3C, and FIG. 7B is a diagram showing a schematic shape of a pulselaser beam used for the heating step shown in FIGS. 3A to 3C;

FIG. 8 is a sectional view illustrating a second heat-treatment;

FIG. 9 is a sectional view of a diffraction grating used for the secondheat-treatment shown in FIG. 8;

FIG. 10 is a typical view of a lamellae formed by the secondheat-treatment;

FIGS. 11A to 11E are typical views illustrating the secondheat-treatment;

FIGS. 12A to 12E are typical views illustrating the secondheat-treatment;

FIG. 13A is a SEM photograph of a sample having been subjected to thefirst heat-treatment, and FIGS. 13B and 13C are EBSP photographs of thesample having been subjected to the first heat-treatment;

FIG. 14 is a diagram showing the degrees of crystal orientations of thesample having been subjected to the first heat-treatment;

FIG. 15 is a diagram showing the degrees of crystal orientations of thesample having been subjected to the first heat-treatment;

FIG. 16 is a view illustrating the crystal orientations of the samplehaving been subjected to the first heat-treatment;

FIGS. 17A to 17C show the results of X-ray analysis of the sample havingbeen subjected to the first heat-treatment;

FIG. 18 is a EBSP photograph of a sample having been subjected to thesecond heat-treatment; and

FIG. 19 is a SEM photograph of the sample having been subjected to thesecond heat-treatment;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the drawings.

In the following embodiments, description will be made by example of amethod of fabricating a semiconductor device unit represented by aliquid crystal display unit 100 shown in FIG. 1.

The liquid crystal display unit 100 includes, on a substrate (notshown), a pixel portion 101 and a peripheral circuit portion 102disposed on the periphery of the pixel portion 101. A liquid crystallayer 103 and a plurality of thin film transistors 104 arrayed in amatrix are formed on the pixel portion 101. The thin film transistors104 are adapted to drive portions, corresponding to respective pixels,of the liquid crystal layer 103. The peripheral circuit portion 102includes a horizontal scanning portion (horizontal scanning circuit orsignal electrode drive circuit) 106 and a vertical scanning portion(vertical scanning circuit or scanning electrode drive circuit) 107. Thehorizontal scanning portion 106 has a video signal terminal 105 and isadapted to feed a horizontal scanning signal together with an inputtedimage signal. The vertical scanning portion 107 is adapted to feed avertical scanning signal to the pixel portion 101.

In this liquid crystal display unit 100, an image signal is fed to thehorizontal scanning portion 106 via the video signal terminal 105, andthe image signal and a horizontal scanning signal are fed from thehorizontal scanning portion 106 to the thin film transistor 104corresponding to each of the pixels of the pixel portion 101; and avertical scanning signal is fed from the vertical scanning portion 107to the thin film transistor 104 corresponding to each of the pixels ofthe pixel portion 101, whereby the liquid crystal layer 103 isswitchingly controlled, to perform image display.

FIGS. 2 to 12E are views illustrating a method of producing acrystalline semiconductor material according to one embodiment of thepresent invention, wherein FIG. 2 is a view showing a structure of asample including an amorphous film 14; FIGS. 3A to 3C are viewsillustrating a first heat-treatment applied to the sample shown in FIG.2; FIG. 4 is a diagram showing one pulse of an excimer laser beam usedfor the first heat-treatment and a second heat-treatment subsequentthereto; FIGS. 5A to 7B are diagrams illustrating a crystalline film 16formed by subjecting the amorphous film 14 to the first heat-treatment;FIG. 8 is a view illustrating a second heat-treatment; FIG. 9 is a viewillustrating a diffraction grating used for the second heat-treatment;and FIGS. 10 to 12E are typical views illustrating a method of forming acrystalline film 17A or 17B by subjecting the crystalline film 16 to thesecond heat-treatment. In addition, FIGS. 5A, 6A, and 7A each show thesurface of the sample, and FIGS. 5B, 6B, and 7B each show a schematicwaveform of a pulse laser beam used for irradiation of the surface ofthe sample.

In the following description, the term “a silicon crystal having {100}orientations” means a silicon crystal preferentially oriented in <100>directions. In the drawings, a silicon crystal (or silicon crystalgrain) having the {100} orientations is often expressed by “Si(100) or(100)”.

First, as shown in FIG. 2, an insulating substrate 11 made from a glassmaterial is prepared. A silicon nitride film 12 made from siliconnitride (SiN_(x): x is a positive number) is formed on the substrate 11to a thickness of 50 nm, and a silicon oxide film 13 made from siliconoxide (SiO₂) is formed on the silicon nitride film 12 to a thickness of120 nm. Each of the silicon nitride film 12 and the silicon oxide film13 is formed by a CVD (Chemical Vapor Deposition) process or asputtering process.

The material of the substrate 11 is not limited to the glass materialbut may be a plastic material. The silicon nitride film 12 and thesilicon oxide film 13 function as protective films for preventing anamorphous film 14 (which is to be converted to a polycrystalline film15, to a crystalline film 16, and further to a crystalline film 17A or17B as will be described later) from being contaminated by impuritiescontained in the substrate 11 made from the glass material.

An amorphous film 14 made from amorphous silicon is formed on thesilicon oxide film 13 by a CVD process, PECVD (Plasma Enhanced ChemicalVapor Deposition) process, or sputtering process. The thickness of theamorphous film 14 is preferably in a range of 10 nm to 200 nm fordesirably forming a crystalline film 16, and a crystalline film 17A or17B in the subsequent crystallization step. In this embodiment, forexample, the amorphous film 14 having a thickness of 40 nm is formed.

In the case of forming the amorphous film 14 by the plasma CVD process,a large amount of hydrogen is contained in the amorphous film 14. Tocope with such an inconvenience, it is preferred to remove hydrogen fromthe amorphous film 14 formed by plasma CVD by heating the amorphous film14 for 2 hr at 450° C. or annealing the amorphous film 14 by a RTA(Rapid Thermal Annealing) process using ultraviolet rays.

[First Heat-Treatment]

The amorphous film 14 is subjected to a first heat-treatment. In thefirst heat-treatment, the surface of the amorphous film 14 is irradiatedwith an energy beam E1 by a plurality of times in an inert gas,typically, a nitrogen atmosphere. The energy beam E1 is exemplified by apulse laser beam emitted from a XeCl excimer laser. To uniformlyirradiate the surface of the amorphous film 14 with the energy beam E1,the energy beam E1 is shaped into a plane beam.

In the first heat-treatment, the energy beam E1 is set to heat theamorphous film 14 (and a polycrystalline film 15, and further acrystalline film 16 to be described later) at such a temperature as topartially melt silicon crystal grains having {100} orientations withrespect to the vertical direction of the substrate 11 and perfectly meltamorphous silicon or silicon crystal grains having face orientationother than the {100} orientations. The setting of such a temperature ofthe amorphous film 14 heated by the energy beam E1 is performed byadjusting parameters of the energy beam E1, specifically, an energydensity, the number of irradiation, and a pulse width of the XeClexcimer laser beam.

Silicon crystal grains having the {100} orientations have melting pointshigher than those of silicon crystal grains having face orientationsother than the {100} orientations. The interface energy between siliconcrystal grains preferentially grown in the {100} orientations and thesilicon oxide film 13 is about 0.01 mJ/cm² smaller than the interfaceenergy between silicon crystal grains preferentially grown in faceorientations other than the {100} orientations and the silicon oxidefilm 13.

Accordingly, assuming that the amorphous film 14 has a thickness of 40nm, the melting points of silicon crystal grains having the {100}orientations are about 0.2° C. higher than those of silicon crystalgrains having face orientations other than the {100} orientations (seeH. A. Atwate et al.: J. Electro Chemical Society 130 (1983) 2050). Thefact that silicon crystal grains having the {100} orientations havehigher melting points is also revealed by a report (W. G. Hawkins etal.: Appl. Phys. Lett. 42 (1983) 358). This report shows that whensilicon is melted by laser irradiation using the ZMR method and themelted silicon is observed in-situ, non-melted residues called lamellaeshaving the {100} orientations are present in a liquid phase.

In view of the foregoing, according to this embodiment, to allowlamellaes having the {100} orientations to remain in a liquid phase ofmelted silicon, the energy density of the energy beam E1 is set to about450 mJ/cm² so as to heat the silicon at such a temperature as topartially melt silicon crystal grains having the {100} orientations andmelt silicon crystal grains having face orientations other than the{100} orientations. It is to be noted that the value of the irradiationenergy of the energy beams E1 contains an error of a measuring devicecaused at the time of measuring the energy.

The number of pulse laser irradiation is set in a range of 10 times to400 times, typically, 150 times. If the number of pulse laserirradiation is less than 10 times, the degrees of the {100} orientationswith respect to the vertical direction of the substrate 11 become verysmall, whereas if the number of pulse laser irradiation is more than 400times, the total amount of evaporation of silicon becomes large.

The XeCl excimer laser is configured as a long pulse laser for emittinga pulse excimer laser beam having a pulse width of, for example, 150 nsas shown in FIG. 4. In the case of irradiating the amorphous film 14having a thickness of 40 nm with one long pulse (pulse width: 150 ns) ofthe pulse laser beam, a solidifying time for solidifying the siliconmelted by the pulse laser irradiation becomes 36 ns. It is to be notedthat the solidifying time is also called a dwelling time for allowing amixing state of a solid phase and a liquid phase of silicon.Accordingly, the probability of bringing the interface between thesilicon oxide film 13 and the melted silicon into a thermal equilibriumstate by such one pulse laser irradiation becomes large, with a resultthat silicon crystals having the {100} orientations occur at theinterface in such a manner as to minimize the energy at the interface.The use of the XeCl excimer laser is effective to lower the processtemperature because the pulse laser irradiation takes only about 150 ns,thereby making it possible to use a plastic material for the substrate.

The pulse interval is set to 0.1 s. Such a pulse interval allows thesilicon melted by the previous pulse laser irradiation to be perfectlysolidified. It is to be noted that according to this embodiment, thesetting of the pulse interval is not important so much.

The conditions of the first heat-treatment are listed as follows:

Irradiation Conditions

-   pulse width: 150 ns-   pulse interval: 0.1 s-   number of irradiation: 150 times-   energy density: about 450 mJ/cm²

The first pulse laser irradiation is made under the above irradiationconditions. At this time, since the energy density of the energy beam E1is set to heat the amorphous film at such a temperature as to partiallymelt the silicon crystal grains having the {100} orientations and meltsilicon crystal grains having face orientations other than the {100}orientations, the amorphous silicon is perfectly melted, to formliquid-phase silicon 21 as shown in FIG. 3A.

In the liquid-phase silicon 21, since the solidifying time for themelted silicon becomes 36 ns during the first pulse laser irradiation,the probability of bringing the interface between the silicon oxide film13 and the melted silicon into a thermal equilibrium state becomeslarge. As a result, silicon crystals 22 having the {100} orientationsoccur at random at the interface in such a manner as to minimize theinterface energy. After the end of the first pulse laser irradiation,the silicon crystals 22 are bonded to each other at random, to formcrystal grains (solid silicon) 23 having the {100} orientations. In thisway, a polycrystalline film 15 composed of polycrystalline silicon,which film partially contains the crystal grains 23 of square shapespreferentially grown in the {100} orientations, is formed as shown inFIG. 5A.

The surface of the polycrystalline film 15 is then subjected to a secondpulse laser irradiation. At this time, in the polycrystalline film 15,the crystal grains 23 having the {100} orientations formed by the firstpulse laser irradiation remain as lamellaes (non-melted residues), andthe other region is melted as described with respect to the first pulselaser irradiation, to form liquid-phase silicon 21 as shown in FIG. 3B.In the liquid-phase silicon 21, as described with respect to the firstpulse laser irradiation, crystals 22 having the {100} orientations occurat random in such a manner as to minimize the energy of the interface.After the end of the second pulse laser irradiation, as described withrespect to the first pulse laser irradiation, the silicon crystals 22are bonded to each other at random, to newly form crystal grains 23having the {100} orientations.

The pulse laser irradiation is further repeated in the same manner asthat of the first and second pulse laser irradiations. At this time, thecrystal grains 23 having the {100} orientations formed by the previouspulse laser irradiation remain as lamellaes (non-melted residues), andin the other region of the liquid-phase silicon 21, crystals 22 havingthe {100} orientations newly occur at the interface between the siliconoxide film 13 and the liquid crystal silicon 21 as shown in FIG. 3C.After the end of the pulse laser irradiation, the silicon crystals 22are bonded to each other at random, to newly form crystal grains 23having the {100} orientations. As a result of repetition of the pulselaser irradiation as shown in FIG. 6B, the number of the crystal grains23 preferentially grown in the {100} orientations with respect to thevertical direction of the substrate 11 becomes large as shown in FIG.6A.

The pulse laser irradiation is further repeated as shown in FIG. 7B, andafter the amorphous film 14 is subjected to the 150th pulse laserirradiation, a crystalline film 16 having square-shaped crystal grainspreferentially grown in the {100} orientations with respect to thevertical direction of the substrate 11 is formed. The grain boundariesof the square-shaped crystal grains of the polycrystalline film 16 arevery sharp as shown in FIG. 7A. The degrees of orientations, offset fromthe {100} orientations by an angle within 10°, is in a range of 80% ormore. On the other hand, in the crystalline film 16, the crystal grainshave various face orientations in the in-plane direction of thesubstrate 11. It is to be noted that lateral crystal growth occurs withthe crystals 22 having the {100} orientations taken as nuclei; however,such lateral crystal growth is negligible as compared with theabove-described crystal growth due to occurrence of the crystals 22having the {100} orientations in the liquid-phase silicon 21.

In this way, according to the first heat-treatment, the amorphous film14 is uniformly subjected to pulse laser irradiation by 150 times insuch a manner as to be heated at such a temperature as to partially meltsilicon crystal grains having the {100} orientations with respect to thevertical direction of the substrate 11 and melt amorphous silicon orcrystal grains having face orientations other than the {100}orientations, to selectively repeat the crystal grain formation step inwhich the crystals 22 having the {100} orientations newly occur at theinterface between the silicon oxide film 13 and the liquid-phase silicon21 and the silicon crystals 22 are bonded to each other at random, tonewly form silicon crystal grains 23 having the {100} orientations. As aresult, the crystalline film 16 having the square-shaped crystal grainspreferentially grown in the {100} orientations with respect to thevertical direction of the substrate 11 is formed, wherein the crystalgrain boundaries of the crystal grains in the polycrystalline film 16become sharp. This makes it possible to enhance the crystallinity of thecrystalline film 16.

Since the first heat-treatment is performed by irradiating the amorphousfilm with a pulse laser beam emitted from the excimer laser, thecrystalline film 16 having good crystallinity can be obtained at a lowtemperature even by using the substrate 11 made from a plastic materialor a glass material.

[Second Heat-Treatment]

The crystalline film 16 obtained by the first heat-treatment issubjected to a second heat-treatment. In the second heat-treatment, asshown in FIG. 8, a diffraction grating 31 functioning as a mask isprovided in such a manner as to be separated from the crystalline film16 by a gap L, and an energy beam E2 emitted from a XeCl excimer laseris projected from above the diffraction grating 31 in a nitrogenatmosphere by a plurality of times. The energy beam E2 is modulated bythe diffraction grating 31, to selectively form, on the crystalline film16, a temperature distribution having maximum temperature regions 16Hand minimum temperature regions 16L whose temperatures are lower thanthose of the maximum temperature regions 16H as shown in FIG. 9. Thetemperature of the minimum temperature region 16L is set to, forexample, such a temperature as to partially melt crystal grains havingthe {100} orientations.

The diffraction grating 31 is made from quartz, and has a plurality ofvery fine grooves. A gap “a” between the adjacent grooves of thediffraction grating 31 is set to 2 μm. The presence of such very finegrooves causes interference between light components diffracted from theadjacent grooves. Assuming that the energy beam E2 is made incident onthe diffraction grating 31 at a variable incident angle θ, a pitch “d”of interference patterns formed on the crystalline film 16 by thediffraction grating 31 is expressed by an equation of d=a/2, which isirrespective of the incident angle θ. That is to say, even if the energybeam E2 is made incident on the diffraction grating 31 at the variableincident angle θ, the pitch of the interference patterns is not affectedby the incident angle θ.

The energy density of the energy beam E2 is set to 450 mJ/cm² so as toheat the minimum temperature region 16L at such a temperature as topartially melt crystal grains having the {100} orientations. With thissetting of the energy density, in the minimum temperature regions 16L,crystal grains having the {100} orientations partially remain aslamellaes 24 (non-melted residues, that is, solid silicon). On the otherhand, in the regions other than the minimum temperature regions 16L,crystal grains having the {100} orientations are perfectly melted, tobecome liquid-phase silicon. At this time, at the solid-liquidinterfaces, each lamellae 24 has the {111} faces as side faces (see FIG.10); however, since the {111} faces of the lamellae 24 are directed inthe maximum temperature gradient directions, and therefore,preferentially oriented toward the solid-liquid interfaces, that is, themaximum temperature regions 16H. As a result, by suitably modulating thetemperature distribution of the crystalline film 16, the orientations ofcrystal grains in the polycrystalline film 16 within the in-planedirection of the substrate 11 can be controlled.

In the case of modulating a pulse laser beam in two orthogonaldirections, a temperature distribution controlled in orthogonal twodirections of the crystalline film 16 is formed by using the diffractiongrating 31 having grooves arranged in a matrix, and pulse laserirradiation is performed under the following conditions. With respect tothe diffraction grating 31, the pitch “a” is set to 2 μm, and the gap Lis set to 150 μm.

Irradiation Conditions

-   pulse width: 150 ns-   pulse interval: 0.1 s-   number of irradiation: 150 times-   energy density: about 450 mJ/cm²

First, as shown in FIG. 11A, the crystalline film 16 obtained by thefirst heat-treatment is prepared. The crystalline film 16 has thecrystal grains preferentially grown in the {100} orientations withrespect to the vertical direction of the substrate 11 and are grown invarious face orientations in the in-plane direction of the substrate 11.A temperature distribution is formed on the crystalline film 16 by usingthe diffraction grating 31 capable of modulating the pulse laser beam inthe orthogonal two directions. To be more specific, as shown in FIG.11B, four maximum temperature regions 16H₂ are formed at four pointsaround each crystal grain (two points on both ends of the extension lineof a diagonal of the crystal grain), and a minimum temperature region16L₂ is formed in a region surrounded by these four maximum temperatureregions 16H₂.

At this time, since the temperature of the minimum temperature region16L₂ is set to the above-described value, by subjecting the crystallinefilm 16 to one pulse laser irradiation, lamellaes 24 having the {100}orientations with respect to the vertical direction of the substrate 11remain. The lamellae 24 is rolled with the {111} faces (side faces)directed toward the maximum temperature regions 16H₂ in a state that the{100} orientations are kept in the vertical direction of the substrate11 as shown in FIG. 1C. After one pulse laser irradiation, crystalgrains are formed by lateral crystal growth with the lamellaes 24 asnuclei. The crystal grains are preferentially grown in the {100}orientations with respect to the vertical direction of the substrate 11,and are preferentially grown in the {100} orientations in the in-planedirection of the substrate 11 as shown in FIGS. 11D and 11E.

As a result of further repetition of pulse laser irradiation, the numberof crystal grains preferentially grown in the {100} orientations in thein-plane direction of the substrate 11 becomes large, and after the150th pulse laser irradiation, a crystalline film 17A having crystalgrains preferentially grown in the {100} orientations with respect tothe vertical direction of the substrate 11 and preferentially grown inthe {100} orientations in the in-plane direction of the substrate 11 isformed. Since the crystal grains are preferentially grown in the {100}orientations in the in-plane direction of the substrate 11, the crystalgrain boundaries in the crystalline film 17A are controlled. It is to benoted that the crystal growth due to occurrence of nuclei having the{100} orientations in the liquid-phase silicon is performed; however,such crystal growth is negligible as compared with the lateral crystalgrowth with the crystal grains having the {100} orientations taken asnuclei.

In the case of modulating a pulse laser beam in one direction, thediffraction grating 31 having grooves arrayed in the one direction isused to form, on the crystalline film 16, a temperature distributioncontrolled in the one direction on the crystalline film 16, and thepolycrystalline film 16 is irradiated with the modulated pulse laserbeam under the following irradiation conditions. With respect to thediffraction grating 31, the pitch “a” is set to 2 μm and the gap L isset to 150 μm.

Irradiation Conditions

-   pulse width: 150 ns-   pulse interval: 0.1 s-   number of irradiation: 150 times-   energy density: about 450 mJ/cm²

First, as shown in FIG. 12A, the crystalline film 16 is prepared. Atemperature distribution controlled in one direction is formed by usingthe diffraction grating 31 capable of modulating a pulse laser beam inthe one direction. The temperature distribution has maximum temperatureregions 16H₁ and minimum temperature regions 16L₁ along the onedirection in such a manner that each of the minimum temperature regions16L₁ is formed between two of the maximum temperature regions 16H₁ asshow in FIG. 12B. The temperature of the minimum temperature region 16L₁is set to such a temperature as to partially melt crystal grains havingthe {100} orientations.

Since the temperature of the minimum temperature region 16L₁ is set asdescribed above, the lamellaes 24 having the {100} orientations withrespect to the vertical direction of the substrate 11 remain non-meltedby one pulse laser irradiation. The lamellae 24 is rolled with the {111}faces (side faces) of the lamellae 24 directed toward the maximumtemperature regions 16H₁ in a state that the {100} orientations of thelamellae 24 are kept in the vertical direction of the substrate 11 asshown in FIG. 12C. After the end of the one pulse laser irradiation,crystal grains are newly formed by lateral crystal growth with thelamellaes 24 taken as nuclei. The crystal grains are preferentiallygrown in the {100} orientations with respect to the vertical directionof the substrate 11 and are preferentially grown in the {110}orientations in the in-plane direction of the substrate 11 as shown inFIGS. 12D and 12E.

As a result of further repetition of pulse laser irradiation, the numberof crystal grains preferentially grown in the {110} orientations in thein-plane direction of the substrate 11 become large, and after the 150thpulse laser irradiation, a crystalline film 17B having crystal grainspreferentially grown in the {100} orientations with respect to thevertical direction of the substrate 11 and preferentially grown in the{110} orientations in the in-plane direction of the substrate 11 isformed. In this polycrystalline film 17B, since the crystal grains havebeen preferentially grown in the {110} orientations in the in-planedirection of the substrate 11, the grain boundaries of the crystalgrains in the polycrystalline film 17B are controlled. It is to be notedthat crystal growth due to occurrence of nuclei having the {100}orientations in the liquid-phase silicon occurs; however, such crystalgrowth is negligible as compared with the lateral crystal growth withthe crystal grains having the {100} orientations taken as nuclei.

In this way, according to the second heat-treatment, the crystallinefilm 16 is irradiated with the energy beam E2 from above the diffractiongrating 31 as a mask by 150 times. In this pulse laser irradiation, thetemperature distribution having the maximum temperature regions 16H andthe minimum temperature regions 16L is selectively formed on thecrystalline film 16, wherein the temperature of the minimum temperatureregion 16L is set to such a temperature as to partially melt the crystalgrains having the {100} orientations. As a result, the lamellae 24occurring upon the pulse laser irradiation is rolled with the {110}faces (side faces) directed to the maximum temperature regions 16H in astate that the {100} orientations of the lamellae 24 are kept in thevertical direction of the substrate 11. The lateral crystal growthoccurs with the lamellaes 24 as crystal nuclei, with a result that thecrystalline film 17A or 17B having crystal grains preferentially grownin the {100} orientations in the vertical direction of the substrate 11and preferentially grown in the controlled orientations in the in-planedirection of the substrate 11 is formed. Accordingly, the crystal grainsin the crystalline film 17A or 17B are not only preferentially grown inthe {100} orientations in the vertical direction of the substrate 11 butalso preferentially grown in the controlled orientations in the in-planedirection of the substrate 11, to control the boundaries of the crystalgrains, thereby enhancing the crystallinity of the crystalline film 17Aor 17B.

Since the second heat-treatment is performed by pulse laser irradiationusing the excimer laser, the crystalline film 17A or 17B having goodcrystallinity can be formed at a low temperature even by using asubstrate made from a plastic material or a glass material.

After formation of the crystalline film 17A or 17B, a liquid crystaldisplay unit including TFTs is fabricated by using the substrate 11provided with such a crystalline film 17A or 17B in accordance with ageneral known method. The process typically includes steps of forming agate oxide film after device isolation, forming a source region and adrain region after formation of a gate electrode, forming an interlayerinsulating film, forming a contact hole, forming metal wiring and ITO(Indium-Tin Oxide), and enclosing liquid crystal. The steps of themethod of producing a crystalline film and the method of fabricating asemiconductor device according to the preferred embodiments are thusended, to accomplish the semiconductor device unit shown in FIG. 1.

The above-described embodiments of the present invention have thefollowing advantages.

The first heat-treatment is performed as follows: namely, the amorphousfilm 14 or the polycrystalline film 15 is uniformly heat-treated by aplurality of times at such a temperature as to partially melt siliconcrystal grains having the {100} orientations with respect to thevertical direction of the substrate 11 and melt amorphous silicon orsilicon crystal grains having face orientations other than the {100}orientations. As a result, it is possible to form the crystalline film16 which has crystal grains preferentially grown in the {100}orientations with respect to the vertical direction of the substrate 11,to form the square-shaped sharp crystal grain boundaries, therebyenhancing the crystallinity. For example, the degrees of orientations,offset from the {100} orientations by an angle within a range of 10°,can be set in a range of 80% or more. In particular, since theheat-treatment is performed by pulse laser irradiation using the XeClexcimer laser, it is possible to form the crystalline film 16 havinggood crystallinity at a low temperature even by using a substrate madefrom a glass material or plastic material, and hence to reduce theproduction cost.

The second heat-treatment is performed as follows: namely, thecrystalline film 16 formed by the first heat-treatment is heat-treatedby a plurality of times in such a manner that a temperature distributionhaving the maximum temperature regions 16H and the minimum temperatureregions 16L whose temperatures are lower than those of the maximumtemperature regions 16H is selectively formed on the crystalline film 16by using the diffraction grating 31, wherein the temperature of theminimum temperature region 16L is set so as to partially melt crystalgrains having the {100} orientations. As a result, the crystal grainboundaries in the in-plane direction of the substrate 11 are controlledin a state that the preferential {100} orientations are kept withrespect to the vertical direction of the substrate 11.

For example, in the case of using the diffraction grating capable ofmodulating the temperature distribution in orthogonal two directions, itis possible to form the crystalline film 17A having crystal grainspreferentially grown in the {100} orientations with respect to thevertical direction of the substrate 11 and preferentially grown in the{100} orientations in the in-plane direction of the substrate 11.Meanwhile, in the case of using the diffraction grating capable ofmodulating the temperature distribution in one direction, it is possibleto form the crystalline film 17B having crystal grains preferentiallygrown in the {100} orientations with respect to the vertical directionof the substrate 11 and preferentially grown in the {110} orientationsin the in-plane direction of the substrate 11.

By using the crystalline film 17A or 17B having good crystallinity forforming a semiconductor device such as a TFT, it is possible to equalizethe quality of the semiconductor device and improve the performancethereof.

While the preferred embodiments of the present invention have beendescribed, the present invention is not limited thereto but may bevariously modified.

For example, in the above-described first heat-treatment, the number ofpulse laser irradiation is set to 150 times, the energy density is setto 450 mJ/cm², and the pulse width is set to 150 ns; however, each ofthe number of pulse laser irradiation, the energy density, and the pulsewidth may be changed insofar as the amorphous film 14 (polycrystallinefilm 15, crystalline film 16) is heated at such a temperature as topartially melt silicon crystal grains, for example, having the {100}orientations with respect to the vertical direction of the substrate 11and melt the amorphous silicon or silicon crystal grains having faceorientations other than the {100} orientations.

In the above-described second heat-treatment, the number of pulse laserirradiation is set to 150 times, the energy density is set to 450mJ/cm², and the pulse width is set to 150 ns; however, each of thenumber of pulse laser irradiation, the energy density, and the pulsewidth may be changed insofar as the temperature of each low temperatureregion of the temperature distribution for forming the crystalline film17A or 17B is set to partially melt the crystal grains having the {100}orientations.

In each of the first and second heat-treatments, the film is heated byusing the energy beam E1 emitted from the XeCl excimer laser; however,the film may be heated by a general electric furnace (diffusion furnace)or another heating means such as a lamp. Further, the XeCl excimer lasermay be replaced by any other laser.

In the embodiments, description has been made by example of the methodof forming the crystalline film 16, 17A, or 17B composed of aquasi-single crystal phase in which a group of square-shapednearly-single crystal grains preferentially grown in the {100}orientations with respect to the vertical direction of the substrate 11are arrayed in a grid shape by the first heat-treatment or the secondheat-treatment; however, crystal grains in the crystalline film 16, 17A,or 17B may be preferentially grown in face orientations other than the{100} orientations.

In the embodiments, description has been made by example of the methodof producing a crystalline semiconductor material represented by thecrystalline film 16, 17A or 17B made from silicon; however, the presentinvention can be applied to a method of producing another crystallinesemiconductor material such as a covalent type semiconductor having adiamond type crystal structure, typically, another group IVsemiconductor. In addition, examples of the group IV semiconductorsinclude silicon, germanium (Ge), carbon (C), and a compoundsemiconductor containing at least one kind selected from a groupconsisting of silicon, germanium, and carbon, for example, SiGe or SiC.

In the embodiments, after the crystalline film 17A or 17B is formed, aTFT is formed by using the crystalline film 17A or 17B and a liquidcrystal display unit is fabricated by using the TFTs in accordance witha known method; however, after the crystalline film 16 is formed, a TFTmay be formed by using the crystalline film 16 and a liquid crystaldisplay unit be fabricated by using the TFTs in accordance with a knownmethod. With this configuration, since the crystalline film 16 is usedfor forming a semiconductor device such as a TFT, it is possible toequalize the quality of the semiconductor device and enhance theperformance thereof.

In the above embodiments, description has been made by example of theliquid crystal display unit 100 as a semiconductor device unit includingsemiconductor devices of the present invention; however, the presentinvention is applicable to another semiconductor device unit includingsemiconductor devices, for example, a solar cell.

The present invention will become more apparent by way of the followingexamples.

EXAMPLE

FIG. 13A is a SEM (Scanning Electron Microscope) photograph of acrystalline film obtained by the first heat-treatment under thefollowing conditions. FIGS. 13B and 13C are EBSP (Electron BackScattering Pattern) photographs of the crystalline film in a normaldirection and a rolling direction, respectively. FIG. 14 is a graphindicating the degrees of the {100} orientations with respect to thevertical direction of a glass substrate after repetition of pulse laserirradiation by 150 times, and FIG. 15 is a graph indicating the degreesof the {100} orientations with respect to the vertical direction of theglass substrate after repetition of pulse laser irradiation by 200times. FIG. 16 is a view illustrating the normal direction (verticaldirection of the glass substrate) and the rolling direction (in-planedirection of the glass substrate) shown in FIGS. 13B and 13C.

In addition, before the SEM photograph of the crystalline film is taken,the crystalline film is subjected to Secco etching. The Secco etching isperformed to increase the sharpness of crystal grain boundaries in thecrystalline film by making use of the characteristic that the etchingrate for a region containing defects is different from that for anotherregion. In the embodiments, a water-solution containing potassiumdichromate (K₂Cr₂O₇), hydrogen fluoride (HF) and water (H₂O) at a mixingrate of 1:2:9 is used as an etching solution for Secco etching.

Sample Structure

amorphous silicon film (thickness: 40 nm)/SiO₂ film (thickness: 120nm)/SiN_(x) film (thickness: 50 nm)/glass substrate

Irradiation Conditions

-   pulse width: 150 ns-   pulse interval: 0.1 s-   number of irradiation: 150 times-   energy density: about 450 mJ/cm²

From the data obtained in the example, it is apparent that as a resultof the first heat-treatment, the amorphous silicon film is crystallized,to form a crystalline film having crystal grains preferentially grown inthe {100} orientations with respect to the vertical direction of theglass substrate. It is also apparent that the degrees of orientations,offset from the {100} orientations by an angle within a range of 10°,becomes 83%, and that the degrees of orientations, offset from the {100}orientations by an angle within a range of 10°, is increased to 96.4% byincreasing the number of pulse laser irradiation to 200 times. It isfurther apparent that the crystal grains are directed in variousorientations in the in-plane direction of the glass substrate.

FIGS. 17A and 17B each show part of the result of X-ray analysis of thesample irradiated with a specific number (50 times, 100 times, and 150times) of pulses of a laser beam. FIG. 17A shows the (111) peak, andFIG. 17B shows the (110) peak. FIG. 17C shows the whole of the result ofX-ray analysis of the sample irradiated with laser beams by 150 times.The data of FIGS. 17A to 17C show that the peak of silicon crystalgrains having the {100} orientations becomes large and the peak ofsilicon crystal grains having the {111} orientations becomes smaller asthe number of pulse laser irradiation becomes large.

FIG. 18 is a EBSP photograph of a crystalline film obtained by thesecond heat-treatment performed, after the first heat-treatment, underthe following conditions by using a diffraction grating capable ofmodulating a pulse laser beam in one direction. The photograph is takenalong the in-plane direction of the glass substrate. The EBSP photographshows that crystal grains in the crystalline film are preferentiallygrown in the {100} orientations with respect to the vertical directionof the glass substrate and preferentially grown in the {110}orientations in the in-plane direction of the glass substrate.

Irradiation Conditions

-   pulse width: 150 ns-   pulse interval: 0.1 s-   number of irradiation: 150 times-   energy density: about 450 mJ/cm²

In this way, it is apparent that the second heat-treatment performed,after the first heat-treatment, by using the diffraction grating capableof modulating a pulse laser beam in one direction, the crystal grains inthe crystalline film are preferentially grown in the {100} orientationswith respect to the vertical direction of the glass substrate andpreferentially grown in the {110} orientations in the in-plane directionof the glass substrate.

FIG. 19 is a SEM photograph of the crystalline film thus obtained. Thephotograph shows that the crystal grain boundaries in the crystallinefilm are also controlled by the first and second heat-treatments. Inaddition, before the SEM photograph of the crystalline film is taken,the crystalline film is subjected to Secco etching.

The present invention configured as described above has the followingeffects:

According to the first method of producing a crystalline semiconductormaterial or according to the first method of fabricating asemiconductor, a crystalline film is formed by uniformly heat-treatingan amorphous material or a polycrystalline material by a plurality oftimes at such a temperature as to partially melt crystal grains having aspecific face orientation with respect to the vertical direction of thesurface of the substrate and melt the amorphous material or crystalgrains having a face orientation other than the specific faceorientation. The crystalline film thus formed has the crystal grainspreferentially grown in the specific face orientation with respect tothe vertical direction of the substrate. As a result, it is possible toform a crystalline film having good crystallinity and hence to fabricatea semiconductor device such as a TFT excellent in equalization andperformance by using such a crystalline film.

In the above-described method, since the heat-treatment is performed bypulse laser irradiation using an excimer laser, it is possible to form acrystalline film having good crystallinity at a low temperature even ona substrate made from a glass material or plastic material, and hence toreduce the production cost.

According to the second method of producing a crystalline semiconductormaterial or the second method of fabricating a semiconductor device, inthe second step, a first crystalline film is formed by uniformlyheat-treating the amorphous material or the polycrystalline material bya plurality of times at such a temperature as to partially melt crystalgrains having a specific face orientation with respect to the verticaldirection of the surface of the substrate and to melt the amorphousmaterial or crystal grains having a face orientation other than thespecific face orientation; and in the third step, a second crystallinefilm is formed by heat-treating the first crystalline film by aplurality of times so as to selectively form, on the first crystallinefilm, a temperature distribution having a high temperature region and alow temperature region whose temperature is lower than that of the hightemperature region, wherein the temperature of the low temperatureregion is set to partially melt the crystal grains having the specificface orientation. Accordingly, in the second crystalline film, thecrystal grains can be preferentially grown in the specific faceorientation with respect to the vertical direction of the substrate andalso preferentially grown in a controlled face orientation in thein-plane direction of the substrate. This makes it possible to controlthe crystal grain boundaries. As a result, it is possible to form acrystalline film having good crystallinity and hence to fabricate asemiconductor device such as a TFT excellent in equalization andperformance by using such a crystalline film.

In the above-described method, since each of the first and secondheat-treatments is performed by pulse laser irradiation using an excimerlaser, it is possible to form a crystalline film having goodcrystallinity at a low temperature even on a substrate made from a glassmaterial or plastic material, and hence to reduce the production cost.

While the preferred embodiments of the present invention have beendescribed using the specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the followingclaims.

1. A method of producing a crystalline semiconductor material,comprising: (a) a first step of forming a starting material on asubstrate, wherein said starting material is selected from the groupconsisting of amorphous semiconductor material and polycrystallinesemiconductor material; (b) a second step of forming a first crystallinematerial comprising crystal grains preferentially grown in the {100}orientation with respect to the vertical direction of the substrate byuniformly heat-treating said starting material by a plurality of times;(c) a third step of forming a second crystalline material byheat-treating said first crystalline material by a plurality of times soas to form, on said first crystalline material, a high temperatureregion and a low temperature region, wherein: (i) the temperature ofsaid low temperature region is lower than the temperature of said hightemperature region; and (ii) the temperature of said low temperatureregion is such as to partially melt said crystal grains having saidspecific face orientation with respect to the vertical direction of thesurface of said substrate.
 2. A method of producing a crystallinesemiconductor material according to claim 1, wherein said startingmaterial comprises at least one material selected from the groupconsisting of silicon (Si), germanium (Ge), and carbon (C).
 3. A methodof producing a crystalline semiconductor material according to claim 2,further comprising the step of forming a silicon oxide film between saidsubstrate and said starting material.
 4. A method of producing acrystalline semiconductor material according to claim 3, wherein saidface orientation is a {100} orientation.
 5. A method of producing acrystalline semiconductor material according to claim 1, wherein saidheat-treatment in said second step is performed by irradiating saidstarting material with a pulse laser beam.
 6. A method of producing acrystalline semiconductor material according to claim 5, wherein saidpulse laser beam is an excimer laser beam.
 7. A method of producing acrystalline semiconductor material according to claim 6, wherein a pulsewidth of said pulse laser beam is set to 150 ns.
 8. A method ofproducing a crystalline semiconductor material according to claim 7,wherein the number of pulse laser irradiation is in a range of 10 timesto 400 times.
 9. A method of producing a crystalline semiconductormaterial according to claim 1, wherein said substrate comprises amaterial selected from the group consisting of glass and plastic.
 10. Amethod of fabricating a semiconductor device comprising: (a) a firststep of forming a starting material on a substrate, wherein saidstarting material is selected from the group consisting of amorphoussemiconductor materials and polycrystalline semiconductor materials; (b)a second step of forming a first crystalline material comprising crystalgrains preferentially grown in the {100} orientation with respect to thevertical direction of the substrate by uniformly heat-treating saidstarting material by a plurality of times; (c) a third step of forming asecond crystalline material by heat-treating said first crystallinematerial by a plurality of times so as to selectively form, on saidfirst crystalline material, a temperature distribution having a hightemperature region and a low temperature region, wherein: (i) thetemperature of said low temperature region is lower than the temperatureof said high temperature region; and (ii) the temperature of said lowtemperature region is such as to partially melt said crystal grainshaving said specific face orientation with respect to the verticaldirection of the surface of said substrate.
 11. A method of producing asemiconductor device according to claim 10, wherein said startingmaterial comprises a material selected from a group consisting ofsilicon (Si), germanium (Ge), and carbon (C).
 12. A method offabricating a semiconductor device according to claim 11, furthercomprising the step of forming a silicon oxide film between saidsubstrate and said starting material.
 13. A method of fabricating asemiconductor device according to claim 12, wherein said faceorientation is a {100} orientation.
 14. A method of fabricatingsemiconductor device according to claim 10, wherein said heat-treatmentin said second step is performed by irradiating said starting materialwith a pulse excimer laser beam.
 15. A method of producing a crystallinesemiconductor material according to claim 1, wherein said temperaturedistribution is formed by modulating a pulse laser beam in one directionin said third step.
 16. A method of producing a crystallinesemiconductor material according to claim 1, wherein said temperaturedistribution is formed by modulating a pulse laser beam in orthogonaltwo directions in said third step.
 17. A method of producing acrystalline semiconductor material according to claim 1, wherein saidtemperature distribution is formed by using a diffraction grating insaid third step.
 18. A method of fabricating a semiconductor device toclaim 10, wherein said temperature distribution is formed by modulatinga pulse laser beam in one direction in said third step.
 19. A method offabricating a semiconductor device according to claim 10, wherein saidtemperature distribution is formed by modulating a pulse laser beam inorthogonal two directions in said third step.
 20. A method offabricating a semiconductor device according to claim 10, wherein saidtemperature distribution is formed by using a diffraction grating insaid third step.